Parent Artery Occlusion for a Giant Serpentine Aneurysm of the Internal Carotid Artery under Electrophysiological Monitoring: A Case Report

Objective: Giant serpentine aneurysms (GSAs) are a rare subtype of giant intracranial aneurysms characterized by partial thrombosis and a tortuous serpentine vascular channel. We report a case of pediatric GSA of the right internal carotid artery (ICA) in which ischemic tolerance was assessed using balloon test occlusion (BTO) with motor-evoked potential (MEP)/somatosensory-evoked potential (SEP) monitoring under general anesthesia, followed by parent artery occlusion (PAO). Case Presentation: A 9-year-old boy was referred to our hospital for decreased right visual acuity detected during a school screening. Imaging revealed a GSA of approximately 39 mm extending from the siphon to the terminus of the right ICA. Under general anesthesia, BTO was performed with concurrent MEP and SEP monitoring. A transient decrease in MEP occurred 18 min after occlusion; however, the waveform recovered immediately with +10% stimulation intensity, and no further MEP deterioration was observed during BTO (total 30 min). PAO of the right ICA was then performed using the double-catheter technique. Postoperatively, the patient developed mild transient left upper limb weakness, and MRI revealed luxury perfusion; both the conditions resolved within a few days without infarct extension. The patient was discharged on postoperative day 10 without any new neurological deficits. Conclusion: This case suggests that when awake BTO is difficult to perform in pediatric patients, BTO with electrophysiological monitoring under general anesthesia can be useful, while highlighting the limitations of MEP monitoring. As a clinical symptom-based assessment is impossible during BTO performed under general anesthesia, a multimodal assessment may further enhance safety when transient MEP deterioration occurs. At present, BTO performed under MEP monitoring should be interpreted as a supplementary assessment to be used only when other alternative methods are unavailable.